c1355493e2c26b613109bfac3dcd898b3acca75a refactor: fees: split fee rate format from fee estimate mode (ismaelsadeeq)
922ebf96ed6674ae7acc6f0cde4d7b064f759834 refactor: move-only: move `FeeEstimateMode` enum to `util/fees.h` (ismaelsadeeq)
Pull request description:
### Motivation
Part of #34075
- The `FeeEstimateMode` enum was responsible for both selecting the fee estimation algorithm and specifying the fee rate' format.
#### Changes in this PR:
* The `FeeEstimateMode` enum (`UNSET`, `ECONOMICAL`, `CONSERVATIVE`) is moved to a new util/fees.h header.
* A new `FeeRateFormat `enum (`BTC_KVB`, `SAT_VB`) is introduced in `policy/feerate.h` for feerate formatting.
* The `CFeeRate::ToString()` method is updated to use `FeeRateFormat`.
* All relevant function calls have been updated to use the new `FeeRateFormat` enum for formatting and `FeeEstimateMode` for fee estimation mode.
This refactoring separates these unrelated responsibilities to improve code clarity.
ACKs for top commit:
l0rinc:
ACK c1355493e2c26b613109bfac3dcd898b3acca75a
furszy:
utACK c1355493e2c26b613109bfac3dcd898b3acca75a
musaHaruna:
ACK [c135549](c1355493e2) — reviewed in the context of PR [34075](https://github.com/bitcoin/bitcoin/pull/34075)
willcl-ark:
ACK c1355493e2c26b613109bfac3dcd898b3acca75a
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a7c29df0e5